J . Org. Chem., Vol. 36, No. 2, 1971 357
NOTES
Registry No.-+a, 26958-30-5; 4b, 26958-31-6; 4c, 26958-32-'7; 4d, 26958-33-8; 4e, 27039-92:5; Sa, 26958-34-9; 5b, 26958-35-0; SC, 27006-05-9; 5d, 26958-36-1; 7,26958-37-23 8,26958-38-3.
SCHEME I n
Viologen Radical from Di(6pyridyl) Ketone Methiodides in Hydroxide1 FELIXE. GEIGER, CHARLES L. TRICHILO, L. MINN,*~ AND NICOLAE FILIPESCU FREDRXCK Department oj' Chemistry, The George Washington University, Washington, D.C. 20006, and Goddard Space Flight Center, NASA, Greenbelt, Maryland 20771 Received August 10, 19YO
The stability of pyridinyl radical cations has made them subject, to intense investigations. Kosower and Cotter reported an interesting formation of dimethylviologen radical 1from 4-cyanopyridinium methiodide and sodium dithionite, presumably via dimerization of the neutral 4-cyanopyridinyl radical intermediateU6 We report here on the unusual formation of the same viologen radical from di(4-pyridyl) ketone monoand dimethiodides (2 and 3) in aqueous hydroxide solution. 0
1
2
3
When 1 M KaOH solutions, thoroughly degassed by numerous freeze-thaw cycles, were mixed under vacuum with crystals of either 2 or 3, the resulting mixture turned deep blue immediately and remained so indefinitely (months). As the color developed, the near-uv-visible absorption showed a parallel increase in the two structured bands characteristic6 of 1, namely, in the visible , , ,A (E) 560 (7450), 602 (10,400), 660 (SSOO), and 730 at nm [16501./(mol cm)] and in the uv at 367 (12,300), 384 (22,300), and 395 nm [34,200 l./(mol cm)]. The blue solutione gave strong esr signals whose presence or absence paralleled that of the color. Examination of high-resolution esr spectra clearly indicated that the blue paramagnetic species formed from both 2 and 3 was dimethylviologen cation r a d i ~ a l . ~The ~ ~ ~experi'~ mental splitting constants for 1 in water, which differ only slightly from those in ethan01,~are 1.33 and 1.59 (1) Taken in part from work done by C. L. T. in partial fulfillment of the P h . D . requirements at The George Washington University. (2) T o whom correspondence should be directed at The George Washington University. (3) P . Borger and A. San Pietro, Arch. Biochem. Biophys., 120, 279 (1967). (4) P. Borger, C. C. Black, and A . San Pietro, Bzochemistry, 6, 80 (1967). (5) 0. Rogne, Biochem. Pharmacol., 16, 1853 (1967). (6) E. M . Kosower and J. L. Cotter, J. Arne?'. Chem. Soc., 86, 5524 (1964). (7) E . M. Kosower and E. J. Poziomek, ibid., 86, 5515 (1964). (8) E. M . Kosower and I . Schwager, ibid., 86, 5528 (1964). (9) C. S. Johnson and H . S. Gutowsky, J. Chem. Phys., S9, 58 (1963). (10) A. H. Corwin, R . R . Arellano, and A. B . Chivvis, Bzochim. Biophus. Acta, 162, 533 (19G3).
Oe for the ring protons, 3.99 Oe for the methyl hydrogens, and 4.25 Oe for the nitrogens; a spectrum simulated by computer,ll with Lorentzian line shape and with a line width of 140 mOe, verified the constants. Radical 1 was generated in a similar manner in nondeaerated samples. Eventually, after months in open sample tubes or much more rapidly upon oxygenation, the blue alkaline solutions turned pale yellow or reddish brown, depending on concentration, and lost their para(11) Modifications to a program b y A. Inzaghi and L. Mongini, European Atomio Energy Commission-Euratom, Report EUR-4064e.
358 J . Org. Chem., Val. 361No. 2,19?’1
magnetism. Preparative scale solutions of either 2 or 3 purposely decolorized with GOZ-freeoxygen produced copious amounts of carbon dioxide upon acidification. An approximate gravimetric evaluation indicated 30 mol % COZyield with respect to original dimethiodide. Furthermore, carbon monoxide was detected with the 1 2 0 5 test for both 2 and 3. The liberated iodine in the case of 3 was determined both colorimetrically and by titration to be about 12 mol %. These observations were useful in the formulation of a reaction mechanism. When the base concentration was lower than -0.1 114, no blue color developed. On the other hand, when the base concentration was very high (-10 ill), the methiodides were no longer soluble and only a very weak blue color developed. Unlike those of its methiodides, sodium hydroxide solutions of the parent dipyridyl ketone remained colorless and diamagnetic under similar conditions. l 2 A plausible mechanism for viologen radical formation from 3 is shown in Scheme I. Although the hydroxide ion could abstract protons from the methyl groups activated by the pyridinium nitrogens, it seems to attack preferentially the carbonyl group, followed by a 1,2 “push-pull” migration of a 4-pyridinium group to generate cation 5 . One can easily visualize proton abstraction from 5 and subsequent facile decarboxylation of zwitterion 6 with formation of the powerful reducing N,N‘-dimethyldihydro-4,4’-bipyridyl(7), agent10~13~14 which is rapidly oxidized by dimethiodide 3 to viologen radical 1. It is known that such molecules as 7, which have also been called “alkali-metal analogs,” are capable of generating viologen radicals in reaction even with common solvent^.^^,^^ We found that radical cation 8 formed by metal reduction of 3 has a long lifetime in degassed acetonitrile. l5 Apparently, however, in aqueous hydroxide it undergoes rapid decarbonylation via 9 and 10, as shown in Scheme I, with ultimate formation of another viologen radical. It is conceivable that radical 8 leads reversibly to 9 with slow leakage over an energy barrier to 10. Presence of both carbon monoxide and carbonate among products together with viologen-radical yields of roughly 50 mol % l a tends to confirm the postulated mechanism. A reaction path for viologen-radical formation from monomethiodide 2 requires decarboxylation, decarbonylation, and either fission a t the carbonyl site with subsequent coupling of 0
0
(12) F. L. Minn, C. L. Trichilo. C. R . H u r t , a n d N. Filipescu, J . Amer. Chem. Soc., 92, 3600 (1970). Preparation and identification of t h e methiodides 2 a n d 8 were also given in this article. (13) F. Miiller and K. A. Bruhn, Ber., 86, 1122 (1953). (14) E. Weitz a n d A . Nelken, Justus Liebigs Ann. Chem., 426, 187 (1921). (15) iY.Filipescu, F. E . Geiger, C . L. Trichilo, and F. L. Minn, J . Phys. Chem., in press. (16) The conversion of the methiodides t o viologen radical was evaluated spectroscopically i n degassed samples of known concentrations from maximum absorbance a t 395 a n d 602 nm.
NOTES N-methylpyridine moieties or acquisition of a second methyl group at the nonmethylated nitrogen. This latter alternative can be visualized as shown in eq 1. However, this possibility should be considered only tentative, since further analytical work may be necessary to substantiate such a mechanism. Registry No.-1, 26988-48-7.
26985-31-9; 2, 26988-47-6; 3,
Acknowledgment.-We thank Professor E. 11. Kosower for helpful suggestions and the Atomic Energy Commission for partial support on Contract AT(40-1)-3797.
A Stereoselective Synthesis of trans-Isobornylc yclohexanol WAYXEI. FANTA* AND WILLIAM F. ERJWN The Procter & Gamble Company, M i a m i Valley Laboratories, Cincinnati, Ohio 46239 Received J u l y I S , 1970
The long-recognized value of sandalwood oil as a perfume essential to the formulation of a variety of fine soap fragrances has prompted us to consider syntheses for other materials reputed to possess sandalwoodlike odors. The curious discovery that a mixture of terpene cyclohexanols, formed by catalytic reduction of the condensation products of camphene and guiacol or camphene and phenol, provides a sandalwood odor first appeared about 20 years ago.’ Although there has been some use of this material in perfumery, it was some years before Demole2 isolated and synthesized the one material responsible for the sandalwood-like odor, trans-3- (ezo-5-isocamphyl)cyclohexanol. Meanwliile, Russian workers reported3 that the somewhat simpler system, trans-3-isobornylcyclohexanol (7) , also possessed a “strong sandalwood” odor. The reported odor properties for trans isomer 7 seemed to mark it as a unique member in a family of similar compounds. Each of the 2- and 4-isobornylcyclohexanols, prepared by others, and 4-bornylcyclohexanoll prepared in these laboratorie~,~ were characterized as almost odorless. Furthermore, the cis-3-isobornylcyclohexanol (8) was claimed to possess a cedar note. Because of what appeared to be very unique and strict structural requirements for the sandalwood odor, we wished to validate this observation through independent synthesis. (1) J. R. Byers, Jr., Amer. Perfumer, 49, 483 (1947); German P a t e n t 834,593 (1952); Chem. Abstr., 47, 5446%(1953). ( 2 ) E. Demole, HeZv. Chim. Acta, 41, 319, 1766 (1964). (3) (a) L. A. Kheifits a n d I. S. Aul’chenko, “Synthese der Reichstoffeaus Terpenphenolen,” Preprint f r o m conference held at Geneva, Nov 17, 1966. (b) L. A. Kheifits and I. 8 . Aul’chenko, Bid. Aktiu. Soedin, 166 (1968); Chem. Abstr, 71, 102026 (1969). (c) KOTE ADDEDIN PROOB.-I. 8. Aul’chenko and L. A . Kheifits. Amer. Perfum., Cosmet., 86, 37 (July 1970). (4) L.A. Kheifits, G, I, Moldovanskaya, A . V. Kokhmanskii, a n d 1’. N. Belov, Zh. Obshch. Khzm., 83, 1676 (1963); Chem. Abstr.. 69, 12845e (1963); G. I. Rloldovanskaya, L. A . Kheifits, A. V. Kokhmanskii, a n d V. K . Belov, Zh. Obshch. Khim., 33, 3392 (1963); Chem. Abstr., 60, 5555h (1964). (5) W. F. Erman, unpublished observations.
